When an automatic tracking system, such as that disclosed in U.S. Pat. No. 4,980,871, directs a video camera for human viewers, there are a number of aesthetic factors which should be considered. In particular, factors such as the centering of the subject within the camera frame, the smoothness of the camera motion against a stable background, and the continuity of the direction of camera motion are all elements which make a video picture aesthetically pleasing to human viewers. Conversely, a video picture which is characterized by abrupt or continuous camera motion and inconsistent camera tracking speed has a tendency to violate a viewer's visual satisfaction criteria.
A typical automated tracking system utilizes a two step process to eliminate any errors between the position of a tracked subject and the camera direction. First, the tracking system measures the angular error between the tracked subject and the orientation of the tracking device/camera. Next, the error information is used to generate a correction signal to control the motion of the tracking device/camera. The new camera position is then utilized in calculating future angular errors. The resulting tracking is mechanical with a tendency to be just as annoying to the viewer as if the tracking was very inaccurate. For example, constant readjustment of the camera position to every motion of the subject can cause rapid eye fatigue in the viewer.
Additionally, typical automated tracking systems use the same tracking strategy and style for all subjects and contexts, whether the subject is giving a lecture or participating in a fast paced athletic event. The inability of such tracking systems to be set to, or alternate between, different styles severely limits their applications.
Unlike an automated tracking system, a human cameraman directs a camera to a subject with less than complete accuracy. The cameraman further adjusts the tracking style according to the context in which the subject moves and the immediate past history of the subject's motions. The resulting video contains minor tracking inaccuracies which are visually more pleasing to a human viewer than the exacting and mechanical tracking of an automated system.
Accordingly, it is an object of the present invention to provide a system which allows a camera to track a moving subject in a manner which is visually and aesthetically pleasing to human viewers, by selectively permitting angular errors between the position of the subject and the direction in which the tracking device/camera is pointing.
Another object of the present invention is to provide a system which allows a camera to track a moving subject in a specific style which is appropriate to the context in which the subject is moving.
A further object of the present invention is to provide a system which allows a camera to track a moving subject in a style which is determined by the system, based on the past history of the subject's motions.